1. Field of the Invention
The invention relates to a control apparatus for use in a vehicle, which has a shift-by-wire type parking mechanism for switching an output shaft of an automatic transmission mounted in, for example, a vehicle such as an automobile, between a lock state where the output shaft cannot rotate and an unlock state where the output shaft can rotate. The invention also relates to a shift-by-wire type parking mechanism for switching the output shaft of the automatic transmission between the lock state where the output shaft cannot rotate and the unlock state where the output shaft can rotate.
2. Description of the Related Art
An automatic transmission is generally designed to allow a driver to slide and operate the slide-type shift lever provided in the driver's seat so as to select, for example, the parking range P, the reverse (reverse travel) range R, the neutral range N, and the drive (forward travel) range D by transmitting the operating force of operating the shift lever directly to the parking mechanism or manual valve through a wire, a rod, or the like.
When the parking range P is selected, the parking mechanism brings an output shaft of the automatic transmission into a lock state where the output shaft cannot rotate. When the reverse range R, the neutral range N or the drive range D is selected, the state of a manual valve, which is one of the components of a shift range switching hydraulic circuit provided in the automatic transmission, is changed to engage or disengage friction engagement elements, such as the clutch and brake of a shifting mechanism portion, whereby the requested range is obtained.
Next, the configuration and operation of the parking mechanism will be described.
The parking mechanism is generally configured by a parking gear, a parking lock pawl, and a parking rod.
The parking gear is fixed externally to the output shaft of the automatic transmission. The parking lock pawl is tiltably supported so as to be displaceable close to or away from the parking gear, and has a pawl capable of being engaged into or disengaged from the teeth of the parking gear. The parking rod is provided with a tapered cone at one end side for tilting the parking lock pawl, and is designed to be displaced forward or backward substantially parallel to the output shaft of the automatic transmission.
This parking rod is driven by a detent lever that drives a manual valve.
The detent lever is tilted by any appropriate actuator. The patterns of driving the detent lever include a pattern called direct operation system in which the detent lever is directly connected to a shift lever through, for example, the wire or rod and so as to move together and driven directly by the operating force of the shift lever, and a pattern which is so-called shift-by-wire system.
In the shift-by-wire system, a sensor, a switch or the like detects a driver's operation of the shift lever, and then the detent lever is driven by any appropriate actuator in response to a shift range signal obtained from the detection (see, for example, Japanese Patent Application Publication No. 5-280637 (JP-A-5-280637), Japanese Patent Application Publication No. 2005-69407 (JP-A-2005-69407)).
Note that in the shift-by-wire system, a joystick, a push button or the like besides the commonly-used shift lever described above is sometimes used as an operating member for outputting a parking request signal or a parking release request signal of the parking mechanism.
When operating the parking mechanism, first the parking rod is displaced backward, for example, by tilting the detent lever, and then the tapered cone pushes up the parking lock pawl so that the pawl of the parking lock pawl is engaged into the teeth of the parking gear, whereby the output shaft of the automatic transmission is brought into the lock state where the output shaft cannot rotate.
When, on the other hand, the parking rod is displaced forward, for example, by tilting the detent lever in a direction opposite to the above direction, the force of the tapered cone pushing up the parking lock pawl is released so that the parking lock pawl is pulled downward by a spring and the pawl is separated from the teeth of the parking gear, whereby the output shaft of the automatic transmission is brought into the unlock state where the output shaft can rotate.
Incidentally, compared to the direct operation system for directly setting the lock state by means of the operating force of the shift lever, in the shift-by-wire type parking mechanism described in the above conventional example, a longer predetermined time lag occurs between reception of a request for bringing the unlocked parking mechanism into the lock state and setting of the lock state. It is therefore desired to reduce this time lag.
This is because there is concern that when, for example, the driver releases the foot brake when his/her vehicle is stopped on a sloping road during a period in which the abovementioned time lag occurs, i.e., in the course from the time when the request is made to the time when the lock state is set, the wheels rotate and the vehicle starts moving depending on the inclination of the road, and consequently the lock state cannot be set easily.